Sprinkle the yeast over warm water. Heat milk, sugar, salt and the 1/2 cup butter together until sugar is dissolved and butter melted. Cool to lukewarm. Add dissolved yeast. Place the flour blended with lemon rind in large mixing bowl; form a well in the center. Add yeast-milk mixture and the eggs. Stir until blended and smooth. Pour into a buttered 9x13-inch baking pan, spreading dough evenly. Let rise in warm place about 45 minutes. Chop the butter into the mixed sugar and cinnamon to form fine particles. Sprinkle over top of risen batter. Add the almonds. Bake in oven preheated to 375 F. for 30 minutes, or until top is golden and syrupy. Makes about 12 servings. Variations: Streuselkuchen: This is much the same as Butterkuchen except that the lemon rind is omitted from the butter and a crumb topping of 1 1/2 cups flour, 3/4 cup sugar, 1/4 cup ground almonds and 8 Tbsp (1 stick) butter are sprinkled over batter. If desired, 1/4 tsp cinnamon may also be added to the topping mixture. Apfebutterkuchen (a Bremen specialty). Prepare as for Butterkuchen, place sliced peeled apples over top of dough before placing in oven. Cover apples with same Butter Topping. Almonds are an optional addition (and very good!).